Photoconductive elements containing alkali-release materials

ABSTRACT

ELECTROPHOTOGRAPHIC ELEMENTS CONTAINING ALKALI-RELEASE MATERIALS ADMIXED WITH PHOTOCONDUCTIVE COMPOSITIONS ARE DESCRIBED. WHEN THESE ELEMENTS ARE DEVELOPED AND HEATED, THE ALKALI-RELEASE MATERIALS GENERATE ALKALINE PRODUCTS WHICH CAUSE A SHIFT IN THE ABSORPTION OF THE SENSITIZERS CONTAINED IN THE PHOTOCONDUCTIVE COMPOSITIONS. SUCH A SHIFT GENERALLY REDUCES THE OPTICAL OPACITY OF THE ELEMENTS, THUS PERMITTING THE ELEMENTS O BE USED AS MASTERS FROM WHICH FURTHER REPRINTS CAN BE MADE.

United, States Patento 3,671,233 PHOTOCONDUCTIVE ELEMENTS CONTAINING ALKALI-RELEASE MATERIALS Lawrence E. Contois, Webster, N.Y., assignor to Eastman Kodak Company, Rochester, NY.

No Drawing. Filed Sept. 2, 1969, Ser. No. 854,748

Int. Cl. G03g 5/06 US. Cl. 961.6 T 12 Claims ABSTRACT OF THE DISCLOSURE Electrophotographic elements containing alkali-release materials admixed with photoconductive compositions are described. When these elements are developed and heated, the alkali-release materials generate alkaline products which cause a shift in the absorption of the sensitizers contained in the photoconductive compositions. Such a shift generally reduces the optical opacity of the elements, thus permitting the elements to be used as masters from which further reprints can be made.

This invention relates to electrophotography and more particularly to novel electrophotographic elements, compositions and methods for producing by electrophotographic processes, elements having improved reprint properties.

The process of xerography, as disclosed by Carlson in US. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material whose electrical resistance varies with the amount of incident actinic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge, generally in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of this surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible by contacting the surface with a suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or in the absence of charge pattern as desired. Deposited marking material can then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, sol-vent vapor, or the like, or transferred to a second element to which it can similarly be fixed. Likewise, the electrostatic latent image can be transferred to a second element and developed there.

It is frequently desirable to employ the image-bearing electrophotographic element as a master from which further prints can be generated. Such elements can be used as masters in many types of reproduction processes. Typical of these processes are the xerographic process, thermographic process, direct electrostatic process, stabilization process, gelatin transfer process, diffusion transfer process, diazo process, etc. A difficulty commonly encountered in the production of copies from sensitized photoconductor-containing coated elements is that the photoconductive element possesses a relatively high optical opacity resulting from coloration imparted by the dye sensitizer in the photoconductor composition. As a result, the element does not transmit suflicient radiation in that portion of the electromagnetic spectrum to which the copy element is sensitive. Therefore, reprints are very difficult to obtain. Also, if'the image-bearing elements are 3,671,233 Patented June 20, 1972 ice to be used for direct reading, the image portions of the elements are often almost indiscernible due to the lack of contrast. There is thus seen to be a need for increasing the radiation-transmitting capability of sensitizing dyecontaining photoconductive elements in the various regions of the electromagnetic spectrum. 7

It is, therefore, an object of this invention to provide novel electrophotographic elements.

It is a further object of this invention to provide novel image-bearing transparent electrophotographic elements useful as masters from which further reproductions can be made.

It is a further object of this invention to provide novel image-bearing transparent electrophotographic elements useful in projection systems.

It is another object of this invention to provide novel photoconductive compositions.

It is still another object of this invention to provide novel processes utilizing the above novel electrophotographic elements and photoconductive compositions of this invention.

These and other objects are accomplished by using an alkali-release material which furnishes alkaline products when thermally decomposed, in conjunction with a photoconductive composition containing a photoconductor, a film-forming polymeric binder and a sensitizing dye for the photoconductor. The photoconductive composition is coated on a support to form an electrophotographic element. The sensitizing dye employed is one which exhibits absorption shifts when subjected to alkaline conditions. Thus, upon heating an electrophotographic element containing an alkali-release material, the heat causes the alkali-release material to decompose to various substances which are alkaline in nature. These products in turn cause the sensitizing dye to undergo an absorption shift. The absorption shift can be small, e.g. 20 nm. or larger, e.g. nm. or more, such that the dye actually undergoes a visible change in color. Since the color of the electrophotographic element is attributable almost entirely to the sensitizing dye, as the sensitizing dye undergoes absorption shifts, the entire element does the same.

There are several advantages resulting from the use of the novel elements of this invention: Image-bearing elements which normally have highly colored backgrounds are made readily viewable according to this invention by causing such background areas to undergo an absorption shift. Generally, such a shift greatly reduces the optical opacity of these background areas so that the image on the element can be easily discerned when using projection techniques. Also, according to this invention such elements can be used as masters from which further reproductions can be generated by xerographic techniques, whereas in the absence of the alkali-release materials the elements are generally unusable as masters because of the high optical opacity of the element.

The theory relating to the reaction between the dye and the alkaline products generated by the alkali-release material is not understood. However, there are two plausible explanations. The first is that the alkaline product chemically alters the dye so that its structure is changed. The new material retains its characteristic of being a sensitizing dye but its region of maximum absorption is shifted from that of the initial dye. A second explanation is that the alkaline products actually destroy completely a portion of the dye rendering it colorless. The residual dye is unaffected but the optical opacity of the element is considerably reduced because of the reduced dye concentration. While any material which has the capability of releasing alkaline components when heated can be used as the alkaline-release material of this invention, the preferred classes of compounds are set forth as follows. AJ

(A) Amidic materials including thiamidic materials such as, but not limited to, the following classes of compounds:

as described in U.S. Patents 2,732,299, 3,046,128, 3,169,067, 3,157,503, British Patent 909,491 wherein R and R each represent:

(a) a lower alkyl group having 1 to 8 carbon atoms such as ethyl, methyl, propyl, butyl, hexyl, cyclohexyl, cyclopentyl and substituted lower alkyl groups such as hydroxyalkyl, aralky1,,nitroalkyl, haloalkyl, aminoalkyl, etc.,

(b) a hydrogen atom,

(c) an aryl group such as phenyl, naphthyl, and typically including substituted aryl groups such as nitroaryl, hydroxyaryl, haloaryl, lower alkyl aryl, lower alkoxy aryl, etc.

(d) a substituted acyl group such as those having the formula wherein R is hydroxy, halogen, e.g. chlorine, 'bromine, etc., hydrogen, aryl, e.g. phenyl, naphthyl, etc., amino including substituted amino, e.g. diloweralkylamino, loweralkoxy having 1 to 8 carbon atoms, e.g. butoxy, methoxy, etc., aryloxy, e.g. phenoxy, naphthoxy, etc., alkyl, e.g. methyl, ethyl, propyl, etc., (e) an amino group having the formula wherein R and R are the same or difierent including hydrogen, lower alkyl having 1 to 8 carbon atoms such as ethyl, propyl, butyl, etc., aryl such as phenyl, naphthyl, etc., halogen, e.g. chlorine, bromine, etc., and

Z represents either an oxygen or a sulfur atom.

/N Rs wherein R R and R have the same significance as R and R defined above;

(3) Rio 0 -S-Rn X- /NH n wherein R R and R have the same significance as R and R 2 defined above, and X- is an anion or acid residue such as chloride, bromide, nitrate, trichloroacetate, perchlorate, carbonate, formate, acetate, aminoacetate;

wherein R R and R have the same significance as R and R defined above and X is the same as defined previously; 7 v

/N io wherein R and R have the same significance as set forth for R and R s g (6) Simple fatty acid amides such as those described in U.S. Pat. 3,255,001; 9

(7) Substituted and polymeric amides such as those described in U.S. Pat. 3,157,503;

(B) Thermolabile salts of a carboxylic acid and an organic base as described in British Patent 998,949 typically having the formula: I

i iiisl wherein D+ represents an organic basic cation having one of the following formulae:

l: I'M:

R2;N CH2 NE: C=NH:]

in which: L represents the atoms necessary to complete a 6 membered heterocyclic nucleus such as a pyridine nucleus, a piperidine nucleus, a morpholine nucleus, etc., including substituted heterocyclic 6 membered nuclei typical substituents being an alkyl group having 1 to 8 carbon atoms, an aryl group and a nitro group; R R and R each represent either a hydrogen atom or an alkyl group preferably having 1 to 8 carbon atoms, e.g. methyl,

ethyl, propyl, butyl, etc., including substituted alkyl groups having 1 to 8 carbon atoms such as:

(g) haloaminoalkyl, e.g. dichloroaminoethyl, N- chloro, N ethylaminopropyl, bromoaminohexyl, etc.,

(h) arylaminoalkyl, e.g. phenylaminoalkyl, diphenylaminoalkyl, N-phenyl, N-ethylaminopentyl, N- phenyl, N chloroaminohexyl, naphthylarninomethyl,

(i) nitroalkyl, e.g. nitrobutyl, nitroethyl, nitropentyl, etc.,

(j) cyanoalkyl, e.g. cyanopropyl, cyanobutyl, cyanoethyl, etc.,

(k) haloalkyl, e.g. chloromethyl, bromopentyl, chlorooctyl, etc.,

(1) alkyl substituted with an acyl group having the formula JLR wherein R is hydroxy, halogen, e.g. chlorine, bromine, etc., hydrogen, aryl, e.g. phenyl, naphthyl, etc., lower alkyl having 1 to 8 carbon atoms, e.g. methyl, ethyl, propyl, etc.,amino including substituted amino, e.g. diloweralkylamino, lower alkoxy having 1 to 8 carbon atoms, e.g. butoxy, methoxy, etc., aryloxy, e.g. phenoxy, naphthoxy, etc.,

R represents either a hydrogen atom, a hydroxyl group or an amino group having the formula wherein R and R are the same or different including hydrogen, lower alkyl having 1 to 8, carbon atoms such as ethyl, propyl, butyl, etc., aryl such as phenyl, naphthyl, etc., halogen, e.g., chlorine, bromine, etc-, R 1, R and R each represent either a hydrogen, atom, an amino group as described above for R or. an alkyl group hav-, ing 1 to 8 carbon atoms including a substituted alkyl group or defined above for R17, R and R n is O, 1 or 2, m is 0, 1, 2 or 3, E and G each represent either a hydrogen atom or a halogen atom such as chlorine, fluorine or bromine, J represents a nitrile group, a trinitratoalkyl group or a trihaloalkyl group such as a trifluoromethyl group, a trichloromethyl group, a tribromomethyl group, a triiodomethyl group, etc.;

(C) Ammonium compounds including quaternary am monium salts, typical compounds being described in U.S. Patents 3,135,607, 2,410,644 and 2,228,562 and having the general formula:

wherein: R is either a hydrogen atom or a lower alkyl group having 1 to 8 carbon atoms such as methyl, ethyl, propyl, butyl, isobutyl, isopropyl, pentyl, etc., and X- is an anion as defined above:

(D) Amine oxides such as those described in U.S. Patent 3,348,947 including those having the formula:

wherein R R and R each represent either of the following.

(1) an alkyl group havingl to 18 carbon atoms, e.g. methyl, ethyl, propyl, butyl, isobutyl, octyl, dodecyl, etc., including a substituted alkyl group having 1 to 18 carbon atoms such as:

(a) alkoxyalkyl, e.g. ethoxypropyl, methoxybutyl,

propoxymethyl, etc.,

(b) aryloxyalkyl, e.g. phenoxyethyl, naphthoxymethyl, phenoxypentyl, etc.,

(c) aminoalkyl, e.g. aminobutyl, aminoethyl, aminopropyl,etc., 1

(d) hydroxyalkyl, e.g. hydroxypropyl, hydroxyoctyl,

hydroxymethyl, etc.,

(e) aralkyl, e.g. benzyl, phenylethyl, etc.,

(f) alkylaminoalkyl, e.g. methylaminopropyl, methylaminoethyl, etc., and also including dialkylaminoalkyl, e.g. diethylaminoethyl, dimethylaminopropyl, propylaminooctyl, etc.,

(g) haloaminoalkyl, e.g. dichloroaminoethyl, N-

chloro N ethylaminopropyl, bromoamino-hexyl,

etc.,

(h) arylaminoalkyl, e.g. phenylaminoalkyl, diphenylaminoalkyl, N phenyl N ethylaminopentyl, N- phenyl N chloroaminohexyl, naphthylaminomethyl,

(i) nitroalkyl, e.g. nitrobutyl, nitroethyl, nitropentyl,

etc.,

(j) cyanoalkyl, e.g. cyanopropyl, cyanobutyl, cyanoethyl, etc.,

(k) haloalkyl, e.g. chloromethyl, bromopentyl, chlorooctyl, etc.,

(1) alkyl substituted with an acyl group having the formula wherein R is hydroxy, halogen, e.g. chlorine, bromine, etc., hydrogen, aryl, e.g. phenyl, naphthyl, etc., lower alkyl having 1 to 8 carbon atoms, e.g. methyl, ethyl, propyl, etc., amino including substituted amino, e.g. dilower-alkylamino, lower alkoxy having 1 to 8 carbon atoms, e.g. butoxy, methoxy,

etc., aryloxy, e.g. phenoxy, naphthoxy, etc., or (2) an aryl group, e.g. phenyl, naphthyl, anthryl, fluorenyl, etc., including substituted aryl groups such as:

(a) alkoxyaryl, e.g. ethoxyphenyl, methoxyphenyl,

propoxynaphthyl, etc.,

(b) aryloxyaryl, e.g. phenoxyphneyl, naphthoxyphenyl, phenoxynaphthyl, etc.,

(0) aminoaryl, e.g. aminophenyl, aminonaphthyl,

aminoanthryl, etc.,

(d) hydroxyaryl, e.g. hydroxyphenyl,

naphthyl, hydroxyanthryl, etc.,

(e) biphenylyl,

(f) alkylaminoaryl, e.g. methylaminophenyl, methylaminonaphthyl, etc., and also including dialkylaminoaryl, e.g. diethylaminophenyl, dipropylaminophenyl, etc.

(g) haloaminoaryl, e.g. dichloroaminophenyl, N-

chloro N-ethylaminophenyl, bromoaminophenyl, etc.,

(h) arylaminoaryl, e.g. phenylaminophenyl, diphenylaminophenyl, N phenyl N ethylaminophenyl, N-phenyl-N-chloroaminophenyl, napththylaminophenyl, etc.,

(i) nitroaryl, e.g. nitrophenyl, nitronaphthyl, nitroanthryl, etc.,

(j) cyanoaryl, e.g.

cyanoanthryl, etc.,

(k) haloaryl, e.g. chlorophenyl, bromophenyl, chloronaphthyl, etc.

I (l) aryl substituted with an acyl group having the formula hydroxycyanophenyl, cyanonaphthyl,

wherein R is hydroxy, halogen, e.g. chlorine, bromine, etc., hydrogen, aryl, e.g. phenyl, naphthyl, etc., amono including substituted amino, e.g. diloweralkylamino, lower alkoxy having 1 to 8 carbon atoms, e.g. butoxy, methoxy, etc., aryloxy, e.g. phenoxy, naphthoxy, etc., lower alkyl having 1 to 8 carbon atoms, e.g. methyl, ethyl, propyl, butyl etc.,

(m) alkaryl, e.g. tolyl, ethyl phenyl, propyl naphthyl, etc.;

7 (E) Amino acids having the formula:

R3(|JH00oH Rae Rs! wherein R R and R each represent hydrogen, an alkyl group as defined above for R 1, R and R or an aryl group as defined above for R R and R29;

(F) Alkali precursors having the general formula:

a: (CH2) 11-1- T as described in U.S. Pat. 3,041,170 wherein: q is an integer from 1 to -6, p is either 1 or 3 depending on the valence of T, T represents an alkali metal such as sodium or potassium, a boron atom or an ammonium radical, R represents a hydrogen atom, a carboxyl group including salts of carboxyl groups such as the sodium, potassium and ammonium salts, an alkyl group as defined above for R R and R or an aryl group as defined above for R27, R23 and R29.

Typical alkali-release materials within the scope of this invention are listed below.

2-hydroxyethylisothiuronium trichloroacetate 2-hydroxypropylisothiuronium trichloroacetate guanidine trichloroacetate methyl urea urea guanidine S-methylthiourea biuret thiosemicarbazide formamide butyramide N-methylacetamide rpiperidinium trichloroacetate tetraethylammonium chloride tetramethylammonium chloride trirnethylamine oxide triethylamine oxide tributylamine oxide N-methyl-morpholine oxide amino butyric acid amino caproic acid sodium formate sodium acetate ammonium carbonate ammonium carbamate ammonium bicarbonate ammonium acetate ammonium formate Also, combinations of two or more of the above described materials can be used.

In preparing typical electrophotographic elements, an alkali-release material is dissolved in a solution containing a film-forming polymeric binder, a s'ensitizer, a photoconductor and a solvent, and then after thorough mixing the resultant composition is coated on an electrically conducting support in a well known manner, such as swirling, spraying, doctor blade coating and the like.

Typical photoconductors useful in this invention are described below. The preferred photoconductors are organic compounds although inorganic materials such as zinc oxide are also operable. Mixtures of two or more photoconductors are also useful.

(A) Arylamine photoconductors including substituted and unsubstituted arylamines, diarylamines, nonpolymeric triarylamines and polymeric triarylamines such as those described in U.S. Pats. 3,240,597 and 3,180,730.

(B) Photoconductors represented by the formula wherein Z represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, binaphthyl, etc.), or a substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a nitro group; Z represents a mononuclear or polynuclear monovalent or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.); or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.gL, methyl, ethyl, propyl, butyl, etc.), an alkoxy grouphaving from 1 to about 6 carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or a nitro group; Q can represent a hydrogen atom or an aromatic amino group, such as ZNI-I; b represents an integer from 1 to about 12, and L represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, analkoxy group, an acyl group, or a nitro group, or a poly(4-vinylphenyl) group which is bonded to the nitrogen atom by a carbon atom of the phenyl group, these materials being more fully described in U.S. Pat. 3,265,496.

(C) Polyarylalkane photoconductors including leuco bases of diaryl or triarylmethane dye salts, 1,1,1 triarylalkanes wherein the alkane moiety has at least two carbon atoms and tetraarylmethanes having an amino group substituted in at least one of the aryl nuclei attached to the alkane and methane moieties of the latter two classes of photoconductors which are non-leuco base materials; andalso other polyarylalkanes included by the formula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent, the aryl groups attached to the central carbon atom being preferably phenyl groups can also be used including substituted aryl groups containing substituents such as alkyl and alkoxy typically having 1 to 8 carbon atoms, hydroxy, halogen, etc., in the ortho, meta or para positions, ortho-substituted phenyl being preferred; the aryl groups can also be joined together or cyclized to form a fluorene moiety, for example; the amino substituent can be represented by the formula wherein each R can be an alkyl group typically having 1 to 8 carbon atoms, a hydrogen atom, an aryl group, or together the necessary atoms to form a heterocyclic amino group typically having 5 to 6 atoms in the ring such as morpholino, pyridyl, pyrryl, etc.; at least one of D, E and G preferably being a p-dialkylaminophenyl group, when I is an alkyl group, such an alkyl group more generally has 1 to 7 carbon atoms, these materials being more fully described in U.S. Pat. 3,274,000,"French Pat. 1,383,461 and in U.S.- Ser. No. 627,857 filed Apr. 3, 1967 by Seus and Goldman now U.S. Pat. No. 3,542,544.

*(D) Photoconductors Comprising 4-diarylamino' substituted chalcones having the formula:

R2 wherein R and R are each phenyl radicals including substituted phenyl radicals, R preferably having the formula:

whereinR and R are each aryl radicals, aliphatic residues of 1 to 12 carbon atoms such as alkyl radicals preferably having 1 to 4 carbon atoms, or hydrogen; particularly advantageous results being obtained when R is a phenyl radical including a substituted phenyl radical and where R is diphenylaminophenyl, dimethylaminophenyl or phenyl, these materials being more fully described in Fox application U.S. Ser. No. 613,846 now US. Pat. No. 3,526,501.

(E) Non-ionic cycloheptenyl compounds which may be substituted with substituents such as:

(1) an aryl radical including substituted as well as unsubstituted aryl radicals,

(2) a hydroxy radical,

(3) a azido radical,

(4) a heterocyclic radical having 5 to '6 atoms in the heterocyclic nucleus and at least one hetero nitrogen atom, and including substituted and unsubstituted heterocyclic radicals, and

(5) an oxygen linked cycloheptenyl moiety.

The substitution on the cycloheptenylnucleus occurs at an unsaturated carbon atom when the cycloheptenyl moiety is a conjugated triene with no aromatic structure fused thereto. However, if there is at least one aromatic structure fused to the cycloheptenyl moiety, then the substituents are attached to a saturated carbon atom. Additional photoconductors within this class are included in one of the following formulae:

D can be any of the substituents defined for E and G above and is attached to a carbon atom in the cycloheptenyl nucleons having a double bond; (R and R (R and R (R and R and (R; and R are together the necessary atoms to complete a benzene ring fused to the cycloheptenyl nucleus; these compounds being more fully described in US. Ser. No. 654,091 filed July 18, 1967 now US. Pat. No. 3,533,786.

(F) Compounds containing an nucleus including:

(1) unsubstituted ands'ubstituted N,N-bicarbazyls containing substituents in either or both carbazolyl nuclei such as:

(a) an alkyl radical including a substituted allryl radical such as a haloalkyl or an alkoxyalkyl radical,

(b) a phenyl radical including a substituted phenyl radical such as a naphthyl, an aminophenyl or a hydroxyphenyl radical,

(c) a halogen atom,

, (d) an amino radical including substituted as well as unsubstituted amino radicals such as an alkyl amino or a phenylalkylamino radical,

(e) an alkoxy radical,

(f) a hydroxyl radical,

(g) a cyano radical,

(h) a heterocyclic radical such as a pyrazolyl, carbazolyl or a pyridyl radical; or

(2) tetra-substituted hydrazines containing substituents which are substituted or unsubstituted phenyl radicals, or heterocyclic radicals having 5 to 6 atoms in the hetero nucleus, suitable results being obtained when all four substituents are not unsubstituted phenyl radicals, i.e., if at least one substituent is asubstituted phenyl radical or a heterocyclic radical having 5 to 6 atoms in the hetero nucleus. Other tetra-substituted hydrazines include those having the following formula:

wherein D E G and l are each either:

(a) a substituted phenyl radical such as a naphthyl radical, an alkyl phenyl radical, a halophenyl radical, a hydroxyphenyl radical, a haloalkylphenyl radical or a hydroxyalkylphenyl radical, or a (b) a heterocyclic radical such as an imidazolyl radical, a furyl radical, or a pyrazolyl radical. In addition J and E can also be (c) an unsubstituted phenyl radical.

Especially preferred are those tetrasubstituted hydrazines wherein both D and G are either substituted phenyl radicals or heterocyclic radicals. These compounds are more fully described in US. Ser. No. 673,962 filed Oct. 9, 1967 now US. Pat. No. 3,542,546.

(G) Organic compounds having a 3,3 bis-aryl-Z- pyrazoline nucleus which is substituted, in either fivemember ring with the same or diiferent substituents. The 1 and 5 positions on both pyrazoline rings can be substituted by an aryl moiety including unsubstituted as well as substituted aryl substituents such as alkoxyaryl, alkaryl, alkaminoaryl, carboxyaryl, hydroxyaryl and haloaryl. The 4 position can contain hydrogen or unsubstituted as well as substituted alkyl and aryl radicals such as alkoxyaryl, alkaryl, alkaminoaryl, haloaryl, hydroxyaryl, alkoxyalkyl, aminoalkyl, carboxyaryl, hydroxyalkyl and haloalkyl. Other photoconductors in this class are represented by the following structure:

wherein: D D';,, 1 and J can be either a phenyl radical including a substituted phenyl radical such as a tolyl radical or a naphthyl radical including a substituted naphthyl radical, E E' G G' L :and L' can be any of the substituents set forth above and in addition can be either a hydrogen atom or an alkyl radical containing 1 to 8 carbon atoms. These organic photoconductors are more fully described in US. Ser. No. 664,642 filed Aug. 31, 1967 now US. Pat. No. 3,527,602.

(H) Triarylamines in which at least one of the aryl radicals is substituted by either a vinyl radical or a vinylene radical having-at least one active hydrogen-containing group. The phrase vinylene radical includes substituted as well as unsubstituted vinylene radicals and also includes those radicals having at least one and as many as three repeating units of vinylene groups such as -CH=CH-) wherein n is an integer of from 1 to 3. Groups which contain active hydrogen are well known in the art, the definition of this term being set forth in several textbooks such as Advanced Organic Chemistry, R. C. Fuson, pp. 154-457, John Wiley & Sons, 1950. The term active hydrogen-containing group as used herein includes those compounds encompassed by the discussion in the textbook cited above and in addition includes those compounds which contain groups which are hydrolyzable to active hydrogen-containing groups. Typical active hydrogen-containing groups substituted on the vinylene radical of the triarylamine includes:

(1) carboxy radicals, (2) hydroxy radicals, (3) ethynyl radicals, (4) ester radicals (e.g.,

wherein R is alkyl or aryl) including cyclic ester radicals (e.g.,

o -R 4 wherein R is a cyclic alkylene radical connected to a vinylene combination such as is found in coumarin derivatives) (5) carboxylic acid anhydride radicals, (6) semicarbazono radicals,

(7) cyano radicals,

(8) acyl halide radicals (e.g.,

etc.), and

(9) amido radicals (e.g.,

wherein R is a hydrogen atom, an alkyl group or an aryl group).

Other active hydrogen-containing groups include substituted and unsubstituted alkylidyne oximido radicals. Photoconductors included in this class can be represented by the following structure:

wherein:

(1) Ar and Ar are each a phenyl radical including a substituted phenyl radical such as a halophenyl radical, an alkyl phenyl radical or an aminophenyl radical,

(2) Ar is an arylene radical including a substituted arylene radical such as a phenylene radical or a naphthylene radical,

(3 )qRm and R are each hydrogen, a phenyl radical including a substituted pheny radical or a lower alkyl radical preferably having 1 to 8 carbon atoms,

(4) X is either:

(a) an active hydrogen-containing group such as a carboxy radical, an acyl halide radical, an amido radical, a carboxylic acid anhydride radical, an ester radical, a cyano radical, a hydroxy radical, a semicarbazono radical, an ethynyl radical, or a methylidyne oximido radical, or

12 (b) hydrogen, provided that when X is hydrogen R and R are also hydrogen, and (5) n is an integer of one to three.

The arylene nucleus can be substituted in any position by the vinyl or vinylene moiety. However, when Ar is phenylene, particularly good results are obtained if the substitution occurs in the p'ara'position. These materials are more fully described in US. Ser. No. 706,800 filed Feb. 20, 1968, now US. Patent 3,567,450.

(I) Triarylamines in which at least one of the aryl radicals is substituted by an active hydrogen-containing group. The term active hydrogen-containing group has the same meaning as set forth above and again includes those compounds encompassed by the discussion in the textbook and additionally includes those compounds which contain groups which are hydrolyzable to active hydrogen-contain ing groups. Typical active hydrogen-containing groups which are substituted on an aryl radical of thetriarylamine include:

(1) carboxy radicals, (2) hydroxy radicals, (3) ethynyl radicals, (4) ester radicals (e.g.,

wherein R is an alkyl or an aryl group), (5) lower alkylene hydroxy radicals (e.g., having 1 to 8 carbon atoms), 7 (6) carboxylic acid anhydride radicals, (7) lower alkylene carboxy radicals (e.g., having 2 to 8 carbon atoms), (8) cyano radicals, (9) acyl halide radicals (e.g.,

0 'l c1 etc.), (10) amido radicals (e.g.,

-i r--N wherein R is a hydrogen atoms, an alkyl group or an y p),

(11) lower alkylidyne oximido radicals having 1 to 8 carbon atoms including substituted alkylidyne oximido radicals (e.g.,

vwherein R is hydrogen or a lower alkyl radical), (l2) semicarbazono radicals, and

(l3) arylene carboxy radicals including substituted arylene carboxy radicals (e.g.,

wherein D and B are phenyl or lower alkyl radicals). Photoconductors' included in this class can be represented by the following structure:

NAr X Al's I wherein:

(a) Ar, and Ar are each a phenyl radical including a substituted phenyl radical such as 'ahalophenyl radical, an alkyl phenyl radical or an amino phenyl radical,

(b) Ar is an arylene radical including a substituted arylene radical such as a phenylene radical or a naphthylene radical, and

() X is an active hydrogen-containing group such as a carboxy radical, an acyl halide radical, an amido radical, a carboxylic acid anhydride radical, an ester radical, a cyano radical, a semicarbazono radical, a hydroxy radical, an ethynyl radical, a met hylidyne oximido radical or a phenylene carboxy radical.

These materials are more fully described in US. Ser. No. 706,780 filed Feb. 20, 1968.

(J) Organo-metallic compounds having at least one aminoaryl substituent attached to a Group IVa or Group Va metal atom. The metallic substituents of this class of organic photoconductors are Group IV a or Group Va metals in accordance with the Periodic Table of the Elements (Handbook of Chemistry and'Physics, 38th edition, pp. 394-95) and include silicon, germanium, tin and lead from Group Na and phosphorus, arsenic, antimony and bismuth from Group Va. These materials can be substituted in the metallo nucleus with a wide variety of substituents but at least one of the substituents must be an amino-aryl radical. The amino radical can be positioned anywhere on the aromatic nucleus, but best results are obtained if the aryl moiety is a phenyl radical having the amino group in the 4 or para position. Typical substituents attached to the metal nucleus include the following:

Photoconductors included in this class can be represented by the following structures:

where E G ,.L and Q can be:

(a) a hydrogen atom,

(b) an aryl radical including unsubstituted as well as substituted arylradicals such as a phenylradical, a naphthyl radical, a dialkylaminophenyl radical,

or a yl mi ph ylrad ca t. t

14 (c) an alkyl radical having 1 to 8 carbon atoms, (d) an alkoxy radical having 1 to 8 carbon atoms, (e) an aryloxy radical such as a phcnoxy radical, (f) an amino radical having the formula wherein R and R can be hydrogen atoms or alkyl radicals having 1 to 8 carbon atoms, or

(g) a heterocyclic radical having 5 to 6 atoms in the hetero nucleus including at least one nitrogen atom such as a triaZolyl, a pyridyl radical, etc.,

T is an amino radical such as an alkylamino radical having 1 to 8 carbon atoms or an arylamino radical such as a phenylamino radical; Ar is an aromatic radical such as phenyl or naphthyl; M and M are the same or dilferent Group IVa metals; M is a Group Va metal; D can be any of the substituents set forth above for E G L and Q and in addition can be a Group IVa organo-metallic radical or, when taken with E, an oxygen atom or a sulfur atom; 1 can be any of the substituents set forth above for E G L and Q and in addition can be when taken with B, an oxygen atom or a sulfur atom. These materials are described in US. Ser. No. 650,664 filed July 3, 1967.

(K) Any other organic compound which exhibits photoconductive properties such as those set forth in Australian Patent 248,402.

Representative organic photoconductors useful in this invention include the compounds listed below: I

TAB LE I diphenylamine dinaphthylamine N,N-diphenylbenzidine N-phenyl-l-naphthylamine N-phenyl-Zmaphthylamine N ,N'-diphenyl-p-phenylenediamine 2-carboxy-5 chloro-4'-methoxydiphenylamine p-anilinophenol N,N'-di-Z-naphthyl-p-phenylenediamine 4,4'-benzylidene-bis-(N,N-dirnetliyl-m-toluidine) triphenylamine N,N,N',N@tetraphenyl m-phenylenediamine 4-acetyltriphenylamine 4-hexanoyltriphenylamine 4-lauroyltriphenylamine 4 hexyltriphenylamine 4-dodecyltriphenylamine 4,4'-bis(diphenylamino)benzil 4,4'-bis(diphenylamino)benzophenone poly [N-4"- (N,N',N-triphenylbenzidine) pol'yadipyltriphenylamine polysebacyltriphenylamine polydecamethylenetriphenylamine poly-N- (4-vinylphenyl)diphenylamine poly-N- (vinylphenyl) -u,a'-dinaphthylamine 4,4'-benzylidene-bis('N,N-diethyl-m-toluidine) 4',4"-diamino-4-dimethylamino-2,2"-dimethyltriphenylmethane 4',4"-bis(diethylamino)-2,6-dichloro-2',2"dimethyltriphenylmethane 4',4"-bis(diethylamino)-2',2"-dimethyldiphenylnaph-- thylmethane 2',2"-dimethyl-4,4',4"-tris(dimethylamino)triphenylmethane 4',4"-bis(diethylamino)-4-dimethylamino-2,2"-dimethyltriphenylrnethane 4',4"-bis(diethylamino)-2-chloro-2',2"-dimethyl-4- dimethylaminotriphenylmethane 4',4"-bis(diethylamino)-4-dimethylamino-2,2',2"-

trimethyltriphenylmethane 1 7 tetra-p-diethylaminophenylplumbane phenyl-di- (p-diethylaminophenyl) phosphine bis (p-diethylaminophenyl) phosphine oxide tri-p-dime thylaminophenylarsine tri-p-diethylaminophenylarsine 2-methyl-4-dimethylaminophenylarsine oxide tri-p-diethylaminophenylbismuthine methyl-d- (p-diethylaminophenyl arsine methyl-di- (p-diethylaminophenyl) phosphine pheny1-tri( p-diethylaminophenyl stannane methyl-tri(p-diethylaminophenyl stannane tetra-p-diethylaminophenylgermane diphenyl-p-diethylaminophenylsilane p-diethylaminophenylarsine tetrakis- [diphenyl- (p-diethylaminophenyl plumbyl] methane tetrakisdiphenyl- (p-diethylaminophenyl sta nnyl] stannane bisphenyl- (p-diethylaminophenyl) ]dibismuthine tri-(p-diethylaminophenyl)phosphine sulfide di- (p-diethylaminophenyl thioxotin Any known sensitizing material can be used in the photoconductive compositions of this invention provided it exhibits absorption shifts under alkaline conditions. It has been found that pyrylium dye salts, that is the pyrylium, thiapyrylium and selenapyrylium salts having the following formula are particularly useful for the purpose:

wherein R, R", and R may each represent an aliphatic group having from 1 to carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, amyl, isoamyl, hexyl, octyl, nonyl, dodecyl, vinyl, styryl, alkoxystyryl, diethoxystyryl, dimethylaminostyryl, 1-butyl-4-pdimethylaminophenyl 1,3 butadienyl, p ethyl 4 dimethylaminostyryl; an alkoxy group such as methoxy, ethoxy, propoxy, butoxy, amyloxy, hexoxy, octoxy, etc.; aryl, such as phenyl, 4-biphenyl, alkphenyl, such as 4-ethylphenyl, 4 propylphenyl, etc., alkoxyphenyl, e.g., 4-ethoxyphenyl, 4 methoxyphenyl, 4 amyloxyphenyl, 2-hex0xyphenyl, Z-methoxyphenyl, 2-amyloxyphenyl, 3,4- dimethoxyphenyl, etc.; w-hydroxy alkoxyphenyl, e.g., 2- hydroxyethoxyphenyl, 3-hydroxyethoxyphenyl, etc.; 4- hydroxyphenyl, halophenyl, e.g., 3,4-dichlorophenyl, 3,4- dibromophenyl, 4-chlorophenyl, 2,4-dichlorophenyl, etc.; azidophenyl, nitrophenyl, etc.; aminophenyl, e.g., 4-diethylaminophenyl, 4- dimethylaminophenyl, etc.; Q is a hetero atom, such as oxygen, sulfur and selenium; and X- is an anionic function.

Typical members of the present pyrylium and thiapyryllium salts include the following:

TABLE II 2,4,6-triphenylpyrylium perchlorate 4-(4-methoxyphenyl)-2,6-diphenylpyrylium perchlorate 4- 2,4-dichlorophenyl -2,6-diphenylpyrylium perchlorate 4-(3,4-dichlorophenyl)-2,6-diphenylpyrylium perchlorate 2,6-bis(4-methoxyphenyl)-4-phenylpyrylium perchlorate 6-(4-methoxyphenyl)-2,4-diphenylpyrylium perchlorate 2-(3,4-dichlorophenyl)-4- (4-methoxyphenyl)-6-pheny1- pyrylium perchlorate 4- (4-amyloxyphenyl -2,6-bis (4-ethylphenyl pyrylium perchlorate 4-(4-amyloxyphenyl)-2,6-bis(4-methoxyphenyl) pyrylium perchlorate 2,4,6-triphenylpyrylium fiuoborate 2,6-bis (4-ethylphenyl -4- 4-methox yphenyl )py rylium perchlorate 2,6-bis 4-ethylphenyl -4- (4-methoxyphenyl pyrylium fluoborate 6-( 3,4-diethoxystyryl)-2,4-diphenylpyry1ium perchlorate 6- (3 ,4-diethoxy-B-amylstyryl -2,4-diphenylpyrylium fluoborate 6-(4-dimethylamino-,B-ethylstyryl)-2,4-diphenylpyrylium fluoborate 6-( 1-n-amyl-4-p-dimethylaminophenyl-1,3 -butadienyl 2,4-diphenylpyrylium fluoborate 6-(4-diemthylaminostyryl)-2,4-diphenylpyrylium fiuoborate,

6-(a-ethyl-;9,;3-dimethylaminophenyl vinylene)-2,4-

diphenylpyrylium fiuoborate 6-( 1-butyl-4p-dimethylaminophenyl- 1,3-butadienyl)- 2,4-diphenylpyrylium fluo'borate 6-(4-dimethylaminostyryl)-2,4-diphenylpyrylium perchlorate 6- [,8,B-bis (4-dimethylaminophenyl) vinylene] -2,4-

diphenylpyrylium perchlorate 2,6-bis(4-dimethylaminostyryl)-4-phenylpyrylium perchlorate 6- (B-rnethyl-4-dimethylaminostyryl)-2,4-diphenylpyrylium fluoborate 6-( 1-ethyl-4-p-dimethylaminophenyl-1,3-butadienyl)- 2,4-diphenylpyrylium fluoborate 6- [(ifi-bis 4-dimethylaminophenyl)vinylene] -2,4-

diphenylpyrylium fiuoborate 6-( 1-methyl-4-p-dimethylaminophenyl-1,3-butadienyl)- 2,4-diphenylpyrylium fiuoborate 4- (4-dimethylaminophenyl) -2,6-diphenylpyrylium perchlorate 2,6-bis(4-ethylphenyl)-4phenylpyrylium perchlorate 2, 6-bis (4-ethylpheny1) 4-methoxyphenylthiapyrylium fluoborate 2,4,6-triphenylthiapyrylium perchlorate 4- (4-methoxyphenyl) -2,6-diphenylthiapyrylium perchlorate 6- 4-methoxyphenyl) -2,4-diphenylthi apyrylium perchlorate 2,6-bis (4-methoxyphenyl) -4-phenylthiapyrylium perchlorate 4-(2,4-dichlorophenyl)-2,6-diphenylthiapyrylium perchlorate 2,4,6-tri(4-methoxyphenyl)thiapyrylium perchlorate 2,6-bis (4ethylphenyl) -4-phenylthiapyrylium perchlorate 4- (4amyloxyphenyl) -2,6-bis (4-ethylphenyl) thiapyrylium perchlorate 6 (4-dimethylaminostyryl) -2,4-diphenylthiapyrylium perchlorate 2,4,6-triphenylthiapyrylium fiuoborate 2,4,fi-triphenylthiapyrylium sulfate 4- (4-methoxyphenyl)-2,6-diphenylthiapyrylium fluoborate 2,4,6-triphenylthiapyrylium chloride 2-(4-amyloxyphenyl)-4,6-diphenylthiapyrylium fiuoborate 4-(4-amyloxyphenyl)-2,6-bis(4-methoxyphenyl)thiapyrylium perchlorate 2,6-bis (4-ethylphenyl -4- (4-methoxyphcnyl thiapyrylium perchlorate 4- (4-diphenylaminophenyl) -2-phenylbenzo [b] thiapyrylium perchlorate 4-anisyl-2,6-bis (4-n-amyloxyphenyl thiapyrylium chloride 2-[QB-bis(4-dimethy1aminopheny1)vinylene]-4,6-

diphenylthiapyryliurn perchlorate 6- 3-ethyl-4-dimethylaminostyryl) -2,4-diphenylthiapyrylium perchlorate 2-(3,4-diethoxystyryl)-4,6-diphenylthiapyrylium perchlorate 2,4,6-trianisylthiapyrylium perchlorate 6-ethyl-2,4-diphenylpyrylium fiuoborate 2,6-bis (4-ethylphenyl -4- (4-methoxyphenyl thiapyrylium chloride,

6- [/3,/3-bis (4-dimethylaminophenyl) vinylene] -2,4-di (4- ethylphenyl) pyrylium perchlorate,

2,6-bis (4-amyloxyphenyl) -4- (4-methoxyphenyl) thiapyrylium perchlorate,

6- 3,4-diethoxy-p-ethylstyryl) -2,4-diphenylpyrylium fiuoborate 6- (4-methoxy-[3-ethylstyryl) -2,4-diphenylpyrylium lfluoborate 2- (4-ethylphenyl) -4,6-diphenylthiapyry1ium perchlorate 2,6-diphenyl-4- (4-methoxyphenyl) thiapyrylium perchlorate 2,6-diphenyl-4- (4-methoxyphenyl) thiapyrylium :fluoborate 2,6-bis (4-ethylphenyl) -4- (4-n-amyloxyphenyl) thiapyrylium perchlorate 2,6-bis(4-methoxyphenyl)-4-(4-n-amy1oxyphenyl) thiapyrylium perchlorate 2,4,6-tri (4-methoxyphenyl) thiapyrylium fluoborate 2,4-diphenyl-6 (3,4-diethoxystyryl) pyrylium perchlorate.

Other useful classes of sensitizing dyes include cyanine, merocyanine, oxonols, styryls, benzylidenes, hemicyanines, hemioxonols, complex cyanines, complex merocyanines, and mixtures thereof including mixtures of the pyrylium dyes.

Preferred binders for use in preparing the present photoconductive layers are film-forming polymeric binders having fairly high dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicone resins; styrene-alkyd resins; silicone-alkyd resins; soyaalkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly- (vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinylbutyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly(n-butylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalkylene terephthalate); phenolformaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates; poly(ethyleneglycol-co-bishydroxyethoxy phenyl propane terephthalate); nuclear substituted vinyl haloarylates such as poly(vinyl metabromobenzoate-co-vinyl acetate); etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in US. Patents 2,361,019 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trade names as Vitel PE-lOl, Cymac, Piccopale 100, Saran F-220, and Lexan 105. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraifin, mineral waxes, etc. Combinations of two or more binders are also useful.

Solvents useful for preparing the coating compositions of the present invention can include a wide variety of organic solvents for the components of the coating composition. For example, benzene; toluene; acetone; 2-butanone; chlorinated hydrocarbons such as methylene chloride; ethylene chloride and the like; ethers, such as tetrahydrofuran and the like, or mixtures of such solvents can advantageously be employed in the practice of this invention.

In preparing the coating compositions utilizing the alkali-release materials disclosed herein, useful results are obtained where the photoconductive substance is present in an amount equal to at least about 1 weight percent of the coating composition. The upper limit in the amount of photoconductive material present can be widely varied in accordance with usual practice. It is normally required that the photoconductive material be present in an amount ranging from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductive material in the coating composition is from about 10 weight percent to about 60 weight percent.

A suitable amount of the alkali-release material and the sensitizing compound are mixed with the coating composition so that, after thorough mixing, they are uniformly distributed throughout the coating composition. The amount of sensitizer that can be added to a photoconductor-incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.0001 to about 30 percent by weight based on the weight of the film-forming photoconductive composition. Generally, a sensitizer is added to the coating composition in an amount from about 0.005 to about 5.0 percent by weight of the total coating composition. The amount of alkali-release material used can vary depending on the particular sensitizer used and the amount of the sensitizer. Also, the amount used depends upon the magnitude of absorption shift desired and also upon the particular alkali-release material employed. Generally, the amount used ranges from about 0.0001 to about 30 percent by weight based on the weight of the film-forming composition. Preferably, the amount ranges from about 0.005 to about 5.0 percent by weight of the photoconductive composition.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a wet coating thickness in the range of about 0.001 inch to about 0.01 inch is useful in the practice of the invention. A preferred range of coating thickness is from about 0.002 inch to about 0.006 inch before drying although such thicknesses can vary widely depending on the particular application desired for the electrophotographic element.

Suitable supporting materials for the photoconductiv layers of the present invention can include any of the electrically conducting supports, for example, conducting papers; aluminum-paper laminates; metal foils, such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass, and galvanized plates; vapor deposited metal layers such as silver, nickel or aluminum on conventional film supports such as cellulose acetate, poly(ethylene terephthalate), polystyrene and the like conducting supports.

An especially useful conducting support can be prepared by coating a transparent film support material such as poly(ethylene terephthalate) with a layer containing a semiconductor dispersed in a resin. A suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of a maleic anhydridevinyl acetate copolymer, cuprous iodide and the like. Such conducting layers and methods for their optimum preparation and use are disclosed in U.S. 3,007,901, 3,245,833 and 3,267,807.

The compositions of the present invention can be employed in photoconductive elements useful in any of the well known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element held in the dark, is given a blanket electrostatic charge by placing it under a corona discharge to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial dark insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the layer by imagewise exposure to light by means of a conventional exposure operation such as, for example, by a contact-printing technique, or by lens projection of an image, or reflex or bireflex techniques and the like, to thereby form a latent electrostatic image in the photoconductive layer. Exposing the surface in this manner forms a pattern of electrostatic charge by virtue of the 21 fact that light energy striking the photoconductor causes the electrostatic charge in the light struck areas to be conducted away from the surface in proportion to the intensity of the illumination in a particular area.

The charge pattern produced by exposure is then developed, i.e., either the charge or uncharged areas rendered visible, by treatment with a medium comprising electrostatically responsive particles having optical density- The developingelectrostatically responsive particles canbe in the form 'of a dust, or powder, and generally comprise a pigment in a resinous carrier called a toner. A preferred method of applying such a toner to a latent electrostatic image for solid area development is by the use of a magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following U.S.' Pats. 2,786,439, 2,786,440, 2,786,441, 2,811,465, 2,874,063,2,984,163, 3,040,704, 3,117,884, and reissue Re. 25,779. Liquid development of the latent electrostatic image may also be used. In liquid development the developing particles are carried to the image-bearing surface in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature, for example, U.S. Pat. 2,297,691 and in Australian Pat. 212,315. In dry developing processes the most widely used method of obtaining a permanent record is achieved by selecting a developing particle which has asone of its components a low-melting resin. Heating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer.

After the latest electrostatic image is rendered visible.

by developing, the absorption characteristic of the element imparted thereto by the sensitizer employed is shifted by heating the element. The heating step is carried The time of such heating can vary from about 0.1 second to 1 hour or more but generally ranges from about 1 second to about minutes. Of course, those skilled in the art will recognize that lower temperatures require longer heating times and higher temperatures require shorter heating times. Also, it will be recognized that the amount of heating utilized will be somewhat dependent upon the nature of the alkali-release material and the nature of the sensitizer. The heating step used for fusing the developer is frequently sufiicient to cause the desired absorption shift.

The compositions of the present invention can be used in electrophotographic elements having many structural variations. For example, the photoconductive composition can be coated in the form of single layers of multiple layers on a suitable opaque or transparent conducting support. Likewise, the layers can be contiguous or spaced having layers of insulating material or other photoconductive material between layers or overcoated -or interposed between the photoconductive layer or sensitizing layer and the conducting layer. It is also possible to adjust the position of the support and conducting layer by placing a photoconductor layer over a support and coating the exposed face of the support or the exposed or overcoated face of the photoconductor with a conducting layer. Configurations differing from those contained in the examples can be useful or even preferred for the same ordifferent application for the electrophotographic element.

The following examples are included for a further understanding of this invention.

.Example 1 photoconductor-bis-p-diethyl-aminotetraphenyl methane-0.5 g.

binder-Vitel PE 101 (a polyester sold by Goodyear Tire and Rubber Co.)-1.5 g.

sensitizer-2,4 bis (4-ethoxyphenyl -6- (4-amyloxystyryl) pyrylium fluoborate-0.0l g.

5 alkali-release material-Z-hydroxyethyl-isothiuronium trichloroacetate-0.005 g.

dichloromethane--10.7 ml.

The resulting compositions is handcoated at a wet thickness of 0.004 inch on two subbed poly(ethylene 1O terephthalate) supports each bearing a conductive layer prepared according to Trevoy, U.S. Patents 3,245,833. The coating blocks are heated to a temperature of 35 C. In a darkened room, the surface of each of the photoconductive layers so prepared is charged to a potential of about +600 volts under a corona charger. The layers are then covered with a transparent sheet bearing a pattern of opaque and light transmitting areas and exposed to the radiation from an incandescent lamp with an illumination intensity of about 75 meter-candles for 12 seconds. One of the resulting electrostatic latent images is developed by conventional electrophotographic liquid developers (e.g., U.S. Patent 2,970,674) and the others by cascading over the surface of the layer a mixture of negatively charged black thermoplastic toner particles and glass beads. When the liquid developer is used, the element is warmed gently to remove residual solvent. A reproduction of the pattern is obtained in each instance. Thereafter, each element is heated to 115 C. for 60 seconds. This heating step causes the alkali-release material to generate alkaline products which in turn cause absorption shifts in the pyrylium dye. As a result of these ---shifts,--thegeneral appearance of the element changes from dark red to pale yellow and has a substantially reduced optical opacity, thus rendering the elements suit- 5...able asa master from which further reprints can be made. To test the reprint capabilities of these imagebearing elements, a conventional diazo film (International Business Machines Type D-l) is exposed through these elements using as the light source the lamp from a diazo processor (3M Filmsort Processor).

.. 'Ihe., exposure .time,is,30.seconds. Upon development of the diazo film in ammonia, a good image on a clear background is obtained. 1

Example 2 Example 1 is repeated except that the alkali-release Example 3 Example 1 is repeated except that the binder employed 1s poly(vinyl-m-bromobenzoate) and the amount of alkali-release material used is 0.0025 g. After heating the image-bearing element to 120 C. for 5 seconds, it is tested for its reprint capabilities in the manner described 6 in Example 1. A good reproduction is obtained.

0 Example 4 Example 3 is repeated except that the alkali-release material is omitted. After development, the element is heated to 120 C. for seconds. Upon testing the element for its reprintability in the diazo printer, no image is reproduced because of the relatively high optical opacity of the element. In this case, heating did not cause an absorption shift.

Example 5 Example 3 is repeated except the photoconductor used is methyl-3-(p-diphenylaminophenyl)propionate and the sensitizer employed is 2,4-bis(4-ethylphenyl)-6-(4-styrylstyryl)pyrylium perchlorate. Once again after developing the latent electrostatic image and heating the element to 23 24 120 C. for seconds, it is tested for its reprint properties NH by the method described in Example 1. The relatively low optical opacity of the element permitted the general f tion of good quality reprints. /NH

Example 6 5 a R t 1. v 7 Example 5 is repeated except that the alkali-release mah i 'R R, R 'R R R R tenal 1s 2-hydroxypropyhsothiuronium trlchloroacetate d R eagh represent a b Selected from the and the photoconductor 1s bis-p-diethylammotetraphenylgroup consisting f lower y radical; hydro. methane. The element bearing the latent electrostatic 10 L gen atom, an aryl radical, a substituted acyl radical Image e p h q and testfid for Its Pf 1m and an amino radical; Z represents an oxygen or sulcharacterlstlcs as described in Example 1. Good reprints fur atom; and X is an anion. v I are Obtalnedv 2. The element of claim 1 wherein the amount of said Example 7 I a alkali-release material in said photoconductive composi- I 15 tion ranges from about 0.0001 to about 30 percent by, Example 3 is repeated except that the alkali-release maweight of said phctoconductive composition. v I terral 1s 0.005 g. of guamdmetnchloracetate. After devel- An electrophoto'gmphic element comprising' a Sup oping and heating, the element has excellent reprint charport having thereon a photoconductive composition which actel'lsncsexhibits absorption shifts under alkaline conditions, said Example 8 20 composition comprising: Example 6 is repeated except that the alkali-release all 0fgani p q on material is methyl urea. After developing the latent eleca g polymeric de trostatic image, the element is heated to 120 C. for 5 a pyl'ylillmvsensitilillg y for Said Photocol'ldllctof seconds. It is then tested for its reprint capability in the which h s absorption Shifts K alkali condimanner described in Example 1. Good reprints are lions, and t 0 obt in d, ((1) an alkali-release material which releases alkaline A summary of the results of the various elements used Products h thfirmally o p d 'a in the above Examples 1 through 8 is represented in the being an amidic material having a formula as folfollowing Table lows:

TABLE III v Alkali- Heatin Visual color of element release material Temp., Time Before After Reprint- Example present 0 (sec.) heating heating ability 115 60 Dark red Pale yellow..- Good. 115 60 tlo Dark red Poor. 120 5 do Pale yellow Good.

120 Dark red Poor. 120 Pale yellow ood. 120 Do. 120 Do. 120 Do.

The invention has been described in detail with partic- R1 ular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications E E can be elfected within the spirit and scope of the invention. C=Z C=NR6 I claim: a NE 1. An electrophotographic element comprising a support having thereon a photoconductive composition 5 which exhibits absorption shifts upon heating, said com- R position comprising: 'H

(a) an organic photoconductor, 1 (b) a film-forming polymeric binder, (c) a sensitizing dye for said photoconductor which NH NH shows absorption shifts under alkali conditions, and 6 5 (d) an alkali-release material which releases alkaline products when thermally decomposed, said material N being an amidic material having a formula as 'fol- G S RH lows:

/NH R1 R1 R1,

Nll' Nll onz o=N1tt 5 V l fi fi wherein 1, 2, 7 a, 9, 10 11, 12 13 14 R and R each represent a member selected from 1W R8 the group consisting of a lower alkyl radical, a hydro- I gen atom, an aryl radical, a substituted acyl radical Q and an amino radical; Z represents an oxygen or sul- NH NH fur atom; and X- is an anion.

m 4. A process for producing an electrostatic latent image N comprising the steps of; 1 a

(a) providing an electrophotographic element com- Ria Rn prising a support having coated thereon a photoconductive composition which exhibitsabsorption shifts upon heating, said composition comprising:

(1) an organic photoconductor,

(2) a film-forming polymeric binder,

(3) a sensitizing dye for said photoconductor which shows absorption shifts under alkaline conditions, and

(4) an alkali-release material which furnishes alkali products when thermally decomposed, said material being selected from the group consisting of amidic materials having a formula as follows:

NH NH C Z C=N Ra NE N6 Rn Ra Rio R13 NH N H CS--Rg X C=NHRn X- Na Na 1 O S R 5 Na 35 Wharein 1, 2 7, 3 9 10, 11, 12, 13 R14, R and R each represent a member selected from the group consisting of a lower alkyl radical, a hydrogen atom, an aryl radical, a substituted acyl radical and an amino radical; Z represents an oxygen or sulfur atom; and X- is an anion;

(b) charging the electrophotographic element,

(c) imagewise exposing the charged electrophotographic element and thereby discharging said electrophotographic element in areas of exposure, and

(d) heating said electrophotographic element to a temperature sufficient to cause said alkali-release material to decompose to alkaline products thereby causing an absorption shift in said sensitizing dye.

5. The process of claim 4 wherein said element is heated to a temperature in the range from about 50 C. to about 150 C.

6. The process of claim 4. wherein said element is heated for a period from about 1 second to about 10 minutes.

7. A process for producing an electrostatic latent image comprising the steps of:

(a) providing an electrophotographic element comprising a support having coated thereon a photoconductive composition which exhibits absorption shifts upon heating, said composition comprising:

(1) an organic photoconductor,

(2) a film-forming polymeric binder,

(3) a sensitizing dye for said photoconductor which shows absorption shifts under alkaline conditions, and

(4) an alkali-release material which furnishes alkaline products when thermally decomposed, said material being selected from the group consisting of amidic materials having a formula as wherein 1 2 7 8 9, 10, 11 12, 13 R R and R each represent a member selected from the group consisting of a lower alkyl radical, a hydrogen atom, an aryl radical, a substituted acyl radical and an amino radical; Z represents an oxygen or sulfur atom; and X- is an anion;

(b) charging the electrophotographic element,

(c) imagewise exposing the charged electrophotographic element and thereby discharging said electrophotographic element in areas of exposure,

(d) developing the resultant recorded electrophotographic image to produce a visible image, and thereafter (e) heating said electrophotographic element to a temperature sufiicient to cause said alkali-release material to decompose to alkaline products thereby causing an absorption shift in said sensitizing dye.

8. The process of claim 7 wherein said element is heated to a temperature in the range from about 50 C. to about C.

9. The process of claim 7 wherein said element is heated for a period from about 1 second to about 10 minutes.

10. An electrophotographic element comprising a transparent support having coated thereon a photoconductive composition comprising:

(a) from about 10% to about 60% by weight of said composition of an organic photoconductor,

(b) a film-forming polymeric binder,

(c) from about 0.005 to about 5.0% by weight of said composition of a pyrylium dye salt sensitizer, and

(d) from about 0.005 to about 5.0% by weight of said composition of methyl urea.

11. An electrophotographic element comprising a transparent support having coated thereon a photoconductive composition comprising:

parent support having coated thereon a photoconductive composition comprising:

(a) from about 10% to about 60% by weight of said composition of an organic photoconductor,

(b) a film-forming polymeric binder,

(c) from about 0.005 to about 5.0% by weight of said composition of a pyrylium dye salt sensitizer, and

27" 28 (d) from about 0.005 to about 5.0% by weight of said 3,476,558 11/1969 Depoorter ,et a1. 961.7 composition of guanidinetrichloroacetate. 3, 8 ,7 9 Fox et a1. 96,-1.6

References Cited CHARLES -E. VAN Piimarj Examiner UNITED STATES PATENTS 5 I. C. COOPER III, Assistant Examiner 3,159,483 12/1964 Behmenburg et a1. 96-1 3,250,615 5/1966 Van Allen ct a1. 96-1 3,418,115 12/1968 Menold et a1. 96-1 961'PC,1v-5,'v1-7,27 

